NP 100 - Mariners Handbook

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CHAPTER 7

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Detection of ice by radar

7.13

1 Though an invaluable aid, the limitations of radar in

detecting ice must always be borne in mind. Absence of an

indication of ice on the radar screen does not necessarily

mean that there is no dangerous ice near the ship. The

strength of the echo received from an iceberg depends as

much on the inclination of its reflecting surfaces as on its

size and range.

2 When approaching the drift ice edge a continuous visual

lookout is essential.

Operators must be aware of the limitations given below

and that less than full operating efficiency will greatly

reduce the chance of detecting ice.

7.14

1 The following conclusions have been reached from

recent experience, but abnormal weather conditions may

substantially reduce detection ranges.

2 In a calm sea, ice formations of all sorts should be

detected; from large icebergs (Photographs 7 and 8,

page 150) at ranges of from 15 to 20 miles down

to small bergy bits at a range of possibly 2 miles.

However, growlers weighing several tons, and

protruding up to 3 m out of the water, are unlikely

to be detected at a range of more than 2 miles. As

warning of ice may therefore be short, radar

should be operated continuously in low visibility

where ice is expected.

3 In any conditions other than calm, it is unsafe to rely

on radar when sea clutter extends beyond 1 mile,

as insufficient warning will be given of the

presence of growlers large enough to damage the

ship, and drift ice becomes confused with sea

clutter.

Fields of concentrated hummocked ice should be

detected in most sea conditions at a range of at

least 3 miles.

4 Ridges show clearly, but shadow areas behind ridges

are liable to be mistaken for leads or the closed

tracks of ships, and the large area of weak echoes

given by a flat floe may be mistaken for a

polynya. It is difficult to distinguish between 10/10

hummocked or rafted ice and 3/10 small floes and

ice cakes.

Large floes in the midst of brash ice (Photograph 2,

page 147) will usually show on radar.

5 A lead through static ice will not show on radar

unless the lead is at least 1 mile wide and

completely free from brash ice.

Areas of open water and smooth floes appear very

similar, but in an ice field the edge of a smooth

floe is prominent, while the edge of open water is

not.

Snow, sleet and rain squalls can sometimes be detected.

Lookouts can then be increased, or speed or course altered

to avoid the squalls.

Signs of open water

7.15

1 Water sky, distinguished by dark streaks on the

underside of low clouds, indicates the direction of leads or

patches of open water. A dark band on the cloud at a high

altitude indicates the existence along this line of small

patches of open water which may connect with a larger

distant area of open water. If low on the horizon, water sky

may possibly indicate the presence of open water up to

about 40 miles beyond the visible horizon.

7.16

1 Dark spots in fog give a similar indication, but are only

visible at considerably shorter distances than reflections on

clouds.

The sound of a surge in the ice indicates the presence of

large expanses of open water in the close vicinity.

A noticeable increase in swell conditions normally

means open ice conditions within 30 miles of the swell.

Effect of abnormal refraction

7.17

1 Ice or open water in the distance may often be detected

by super-refraction (5.52) raising the horizon. The image of

the ice or areas of open water, or a mixture of the two,

may be seen as an erect or inverted image. Alternatively,

both images may be seen at once, one above the other and

usually in contact, in which case the erect image is the

higher of the two. Allowance must be made for the fact

that the refraction causing the mirage will increase the

apparent dimensions of small ice, sometimes so greatly as

to make small pieces appear like icebergs. The areas of

open water are dark relative to the ice.

THE MASTER’S DUTY REGARDING ICE

Avoidance

7.18

1 The International Convention for the Safety of Life at

Sea (SOLAS), 1974, requires the Master of every ship,

when ice is reported on or near his track, to proceed at a

moderate speed at night or to alter course to pass well

clear of the danger zone.

Reports

7.19

1 He is also required to make the following reports:

On meeting dangerous ice:

Type of ice;

Position of the ice;

UT (GMT) and date of observation.

2 On encountering air temperatures below freezing

associated with gale force winds causing severe ice

accumulation on ships:

Air and sea temperatures;

Force and direction of the wind;

Position of the ship;

UT (GMT) and date of observations.

ICE REPORTS

Extent

7.20

1 Ice reports are available when ice is prevalent for the

Arctic, Iceland, Baltic Sea, E coast of Canada, Gulf of

Saint Lawrence, Gulf of Alaska, Bering Sea, Sea of

Okhotsk, Sea of Japan and Antarctica. Some of these are

Facsimile reports. The Canadian Ice Reconnaissance

Aircraft Facsimile Service operates for both the winter and

summer navigation seasons. Details of these reports and the

radio stations transmitting them are given in Admiralty List

of Radio Signals Volume 3.

International Ice Patrol

7.21

1 The United States Coast Guard operates the International

Ice Patrol, the cost being met by Signatory Nations to the

1974 SOLAS Convention. Its prime object is to warn ships

of the extent and limits of icebergs and sea ice in the

North Atlantic near the Grand Banks of Newfoundland.

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The service operates during the ice season from late

February or early March to about the end of June.

For details, see Admiralty List of Radio Signals Volume

3(2).

ICE ACCUMULATION ON SHIPS

General information

7.22

1 In certain conditions ice, formed of fresh water or sea

water, accumulating on the hulls and superstructures of

ships can be a serious danger.

Ice accumulation may occur from three causes:

Fog, including fog formed by evaporation from a

relatively warm sea surface, combined with

freezing conditions;

2 Freezing drizzle, rain or wet snow.

Spray or sea water breaking over the ship when the

air temperature is below the freezing point of sea

water (about –2°C).

Icing from fresh water

7.23

1 From fog, drizzle, rain or snow, the weight of ice which

can accumulate on the rigging may increase to such an

extent that it is liable to fall and endanger those on deck.

Radio and radar failures due to ice on aerials or

insulators may be experienced soon after ice starts to

accumulate.

The amount of ice, however, is small compared with the

amount which accumulates in rough weather with low

temperatures, when heavy seas break over a vessel.

Icing from sea water

7.24

1 When the air temperature is below the freezing point of

sea water and the ship is in heavy seas, considerable

amounts of water will freeze on to the superstructure and

those parts of the hull which are sufficiently above the

waterline to escape being frequently washed by the sea.

The amounts so frozen to surfaces exposed to the air will

rapidly increase with falling air and sea temperatures, and

have in extreme cases lead to the capsizing of vessels.

2 The dangerous conditions are those in which strong

winds are experienced in combination with air temperatures

of about –2°C or below; freezing rain or snowfall increases

the hazard. The rapidity with which ice accumulates

increases progressively as the wind increases above force 6

and as the air temperature falls further below about –2°C.

It also increases with decreasing sea temperatures. The rate

of accumulation also depends on other factors, such as the

ship’s speed and course relative to the wind and waves,

and the particular design of each vessel.

Forecasting icing conditions

7.25

1 Extensive observations have been made of ice

accumulation due to sea water, mainly on fishing vessels

around Iceland, Greenland, Labrador, and in the Barents

Sea and North Pacific Ocean. The nomograms in Diagram

7.25 are derived from the work of J.R. Overland, C.H.

Pease, R.W. Preisendorfer and A.L. Comiskey. They

indicate the rate of ice accumulation to be expected on a

slow moving vessel with the wind ahead or on the beam.

They are for different values of wind speed and air

temperature at a selection of sea temperatures. They are

reproduced by permission of NOAA/Pacific Environmental

Laboratory.

Avoiding ice accumulation

7.26

1 It will be appreciated that it is very difficult to forecast

accurately the three variables involved. Furthermore, the

region of icing often moves at such a rate that vessels

cannot take evasion action unless warning of impending

icing conditions is received.

2 The mariner is therefore advised to exercise all possible

caution whenever gales are expected in combination with

air temperatures of –2°C or below. These conditions are

most likely to occur with winds from polar regions, but the

direction may be any that will transport sufficient cold air.

If these conditions are expected, the prudent course is to

steer towards warmer conditions, or to seek shelter, as soon

as possible.

3 If unable to reach shelter or warmer conditions, it has

been found best to reduce spray to a minimum by heading

into the wind and sea at the slowest speed possible, or if

weather conditions do not permit that, to run before the

wind at the least speed that will maintain steerage way.

For Obligatory Reports on encountering severe icing, see

7.19.

OPERATING IN ICE

General rule

7.27

1 Ice is an obstacle to any ship, even an ice breaker. The

inexperienced ice navigator is advised to develop a healthy

respect for the latent power and strength of ice in all its

forms. However, well-found ships in capable hands can

operate successfully in ice-covered waters.

2 The first principle of successful passage through ice is

to maintain freedom of manoeuvre. Once a ship becomes

trapped, she goes wherever the ice goes. Operating in ice

requires great patience and can be a tiring business with or

without icebreaker escort. The ice-free long way round a

difficult area whose limits are known, is often the quickest

and safest way.

3 In ice concentrations three basic ship handling rules

apply:

Keep moving, even if very slowly;

Try to work with the ice movement and not against it;

Excessive speed leads to ice damage.

Ice identification

7.28

1 Caution. Before attempting any passage through ice it is

essential to determine its type, thickness, hardness, floe size

and concentration (6.16). This can only be done visually.

It is very easy and extremely dangerous to underestimate

the hardness of ice.

After a snow fall ice can be very difficult to identify.

The utmost caution and experience is required then when

making a passage through the ice.

Ice is seldom uniform. There can be different types of

ice in drift ice.

Changes in ice conditions

7.29

1 Ice moves continually under the influence of wind and

current, floating ice is much influenced by the wind. With

a change of wind, ice conditions can completely change,

sometimes within hours.

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-4

-8

-12

-16

-20

(°C)

(°F)

Wind Speed (m/s)

Wind Speed (Knots)

Sea Temperature +1°C

Wind Speed (Knots)

Sea Temperature +5°C

Wind Speed (Knots)

Sea Temperature +3°C

Wind Speed (Knots)

Sea Temperature +7°C

ICING CONDITIONS

For vessels with the wind ahead of or on the beam

Icing Nomograms (7.25)

Light Icing Less than 0.7cm/hour

Moderate Icing 0.7-2.0cm/hour

Heavy Icing Greater than 2cm/hour

Air Temperature

Light

Moderate

Heavy

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2 Ice fuses when the temperature falls below freezing. An

area of separate ice floes and loose fragments can quickly

turn into a solid mass of ice and pose serious problems,

even for ice breakers.

When practicable, a look-out from aloft will frequently

detect distant leads and open water invisible from the

bridge.

Considerations before entering ice

7.30

1 Ice should not be entered if an alternative, although

longer, route is available.

Before deciding to enter the ice the following factors

need to be considered:

Type of ice;

Time of year, weather and temperature;

Area of operation;

Availability of icebreakers;

2 Vessel’s ice class in relation to the type of ice

expected;

State of hull, machinery and equipment, and quantity

of bunkers and stores left;

Draught and depth of water over the propeller tips

and the rudder;

Ice experience of the person in charge on the bridge.

7.31

1 Thin new ice allows passage to be made through it by

modern steel vessels on the original intended route.

Thick first year ice or old ice which cannot be

negotiated considering the ice class of the vessel, requires

the prudent mariner to stop and wait until either conditions

improve with a change of wind or tide, or an icebreaker is

available.

Passage through ice

Making an entry

7.32

1 The following principles govern entry into the ice:

Where the existence of pressure is evident from

hummocking and rafting, entry should never be

attempted;

The ice should be entered from leeward, if possible.

The windward edge of an icefield is more compact

than the leeward edge, and wave action is less on

the leeward edge;

2 The ice edge often has bights separated by projecting

tongues. By entering at one of the bights, the surge

will be found to be least.

Ice should be entered at very low speed and at right

angles to the ice edge to receive the initial impact,

and once into the ice speed should be increased to

maintain headway and control of the ship.

Drift ice

7.33

1 Ice masses of thick broken ice, especially those that bear

signs of erosion by the sea on their upper surface, should

be avoided. They have underwater spurs, extraordinarily

strong and hardly affected by melting.

If a large floe blocks the ship’s intended course, no

attempt should be made to break it unless it is very rotten.

It is best to go round it, if possible, or to put the stem

against it, to increase power until the floe is forced ahead

and begins to swing to one side, when power should be

reduced to allow it to pass clear.

2 If collision with a floe cannot be avoided, it should be

hit squarely with the stem. A glancing blow may damage

the bow plating, and by throwing the ship off course cause

another glancing blow from a nearby floe, or her stern to

be swung into the ice damaging her rudder and propellers.

If navigating in an extensive area of thin or light ice,

the navigator, particularly in Polar Waters, may suddenly

come upon floes or fragments of hard ice that may be

interspersed among the light ice.

3 At night or in reduced visibility when passing through

areas where ice is present, speed must be reduced or the

ship stopped until the mariner can see and identify the ice

ahead of the ship. Navigation in ice after dark should not

normally be attempted: if it is attempted, good searchlights

are essential.

7.34

1 Icebergs in an icefield. All forms of glacial ice and

dirty ice broken away from coastal regions should be given

a wide berth.

Icebergs are usually current-driven while the icefield will

have a wind drift component (6.12).

With a strong current icebergs may travel upwind, when

open water will be found to leeward, and piled up pressure

to windward of the iceberg which may endanger a vessel

unable to work clear. Similar conditions have been

observed with a weak current and a strong wind, when the

floes overtaking an iceberg were heaped up to windward,

while a lane of open water lay to leeward of the iceberg.

2 In traversing drift ice, advantage may be taken of leads

created by the movement of icebergs through a

wind-compacted belt of ice.

It should be appreciated by the Master of any ship beset

in drift ice, in the presence of bergs/bergy bits, that all

relative motion is likely to be due to the drift ice in

motion. All ices of lane origin will be static.

For caution on dangers near icebergs, see 6.17.

Leads

7.35

1 Every opportunity should be taken to use leads through

ice, but when not accompanied by an icebreaker, it is

unwise to follow a shore lead with an onshore wind

blowing.

A ship stopped in ice close inshore should always be

pointed to seaward unless it is intended to anchor.

Speed in ice

7.36

1 The force of the impact on striking ice, depends on the

vessel’s tonnage and speed. It varies as the square of the

speed.

Speed in ice therefore requires careful consideration. If a

vessel goes too slowly she risks being beset, if too fast she

risks damage from collision with floes.

2 Where concentrations of ice vary, and a ship passes

from close ice, through a small patch of light ice of clear

water, to more close ice, engine revolutions should be

reduced on entering the more open patch. If revolutions are

maintained, the ship will gather way as she passes through

the clearer water, and be carrying too much way for

re-entering the close ice.

Use of engines and rudder

7.37

1 Engines must be prepared to go full astern at any time.

Propellers are the most vulnerable part of a ship.

7.38

1 Ships should go astern in ice with extreme care, and

always with the rudder amidships. If a ship is stopped by a

heavy concentration of ice, the rudder should be put

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amidships and the engines kept turning slowly ahead. This

will wash the ice astern clear, and enable the ship to come

astern, after making certain that the propellers are clear of

ice. If ice goes under a ship, speed should immediately be

reduced to dead slow.

2 Violent rudder movements should only be used in

emergency. They may swing the stern into the ice,

particularly in patches of clear water or leads during

passage through the ice.

3 Frequent use of the rudder, especially in the hard-over

position, has the effect of slowing down the vessel’s

passage through ice. This can often be used to advantage to

reduce speed without the loss of steerage way resulting

from reducing the engine revolutions. Too much rudder,

however, when pushing through ice or following an ice

breaker, may bring the vessel to a complete stop.

Anchoring

7.39

1 In a heavy concentration of ice anchoring should be

avoided.

If ice is moving, its tremendous force may break the

cable. When conditions permit anchoring, such as in light

brash ice, rotten ice, or among widely scattered floes, the

windlass and main engines should be kept at immediate

notice, and the anchor weighed as soon as wind threatens

to move ice on to the ship.

Ramming and backing

7.40

1 Forcing a passage through heavier ice to reach open

water, or an area where ice is less heavy, may sometimes

be justified. The method is to ram the ice to break it by

sheer impact and weight, and then to back out of the ice

into the water and broken ice astern. To avoid the risk of

being embedded in the ice, the engines should be going

astern before the vessel stops. However, to avoid propeller

and rudder damage, the engines should be going ahead

before any stern contact with ice takes place.

2 By repeatedly carrying out this procedure, slow progress

ahead can sometimes be made. It is not advisable, however,

to continue forcing the passage unless the channel so made

considerably exceeds the beam of the vessel to allow her to

move freely out astern.

3 Caution. The procedure is dangerous and should be

used with the utmost discretion as heavy damage to a

vessel can result. Only in extreme emergency should it be

used by vessels with low or no ice class or those with a

bulbous bow.

Beset

7.41

1 The most serious danger is from pressure of the ice

which may crush the hull or nip off the ship’s bottom. This

risk is greater in ice concentrations of 7/10 or more.

2 A ship beset in drift ice is at risk from drifting with the

moving ice against icebergs, ice fronts, shoals and the

shore: every precaution should be taken to avoid this

situation. If the lee of an iceberg can be made whilst being

swept along, it will provide safe shelter, but the possibility

of the iceberg capsizing, or being held by a shoal, must be

borne in mind.

3 It should be appreciated by the Master of any ship beset

in drift ice, in the presence of bergs/bergy bits, that all

relative motion is likely to be due to the drift ice in

motion. All ices of lane origin will be static.

7.42

1 When a ship proceeding independently becomes beset it

usually requires icebreaker assistance to free her. However,

a ship can sometimes be freed by going full ahead and full

astern alternately with full helm one way and then the

other in order to swing her, this may loosen the ship

sufficiently to enable her to move ahead through the ice. If

the ship starts moving astern, the rudder must be

amidships.

2 Alternatively, ships can sometimes free themselves by

pumping and transferring ballast from side to side, and it

may need very little change in trim or list to release the

ship.

3 Other alternatives are: to take an anchor or warp to the

ice astern, leading the cable through fairleads to the

windlass, and to take the strain with the engines going full

astern; or to lay out anchors on each beam and heave first

on one and then on the other with the engines going full

astern.

Dead reckoning

7.43

1 Whilst GPS, DGPS and GLONASS systems have much

reduced the need, a careful reckoning should be kept of all

alterations of course and speed together with the times at

which they were made, so that a large scale plot of the

ship’s track can be maintained. The lack of information on

tides and other factors usually prevents the most accurate

dead reckoning from giving the exact position of the ship,

but a carefully kept reckoning will considerably help to

avoid errors.

2 Icebergs, which can be regarded as stationary, can be of

great value as temporary marks in maintaining the dead

reckoning position. They may also mark shoals.

3 In keeping the reckoning, the fundamental factors, speed

and course, change continually and do not lend themselves

to accurate calculation. Even if a gyro compass and

automatic pilot are fitted, the speed relative to the ice is

required, and this can rarely be measured continuously with

accuracy. To check the resultant of the ship’s course and

speed through the ice, and the drift of the ice, every

opportunity should be seized to obtain fixes or observed

positions. The speed at any moment can be measured by

timing the passage of an ice floe down a known length of

the ship’s side, like a Dutchman’s log. The speed through

the ice should be obtained as often as possible, or at least

twice an hour.

Sights

7.44

1 Sights must be taken with great care, for in ice false

horizons are frequently observed. It is normal in polar

regions for the atmosphere to differ considerably from the

standard, particularly near the sea surface. This affects both

refraction and dip. Refraction variations of 2° or more are

not uncommon and an extreme value of 5° has been

reported. The sun has been known to rise as much as ten

days before it was expected. A wise precaution is to apply

corrections for air temperature and atmospheric pressure,

particularly for altitudes of less than 5°. Because of the low

temperature, the refraction correction for sextant altitudes

may require to be taken from the appropriate table in the

Nautical Almanac.

2 If the horizon is covered with ice, it may still be used

for celestial observations by subtracting the height of the

ice on the horizon above the water from the height of eye

of the observer: the maximum error this may cause is 4′. A

bubble sextant, or a sextant used with an artificial horizon

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set up on the ice, will be found, however, to give better

results. It should be remembered, however, that refraction

elevates both the celestial body and the visible horizon, so

that the error due to abnormal refraction is minimised if the

visible horizon is used for observations. Ice shelves on the

horizon may require an ability to obtain a position line by

’back angle’ sights.

ICEBREAKER ASSISTANCE

Control

7.45

1 Masters of icebreakers are highly skilled and

experienced in the specialist fields of ice navigation,

icebreaking and ice escorting. It is therefore the Master of

the icebreaker who directs any ice escorting operation.

Icebreakers use air reconnaissance, when available, to

locate leads and open water. Some carry helicopters which

are able to guide ships, by direct communication, along the

best routes through the ice.

2 Escorted vessels must:

Follow the path cleared by the icebreaker and not

venture into the ice on their own;

Have towing gear rigged at all times.

Have Officers on the bridge thoroughly acquainted

with the Icebreaker Signals given in The

International Code of Signals.

Acknowledge and execute promptly signals made by

the icebreaker, whether by RT, light or sound.

3 After requesting icebreaker assistance, a ship must

maintain continuous radio watch, and keep the icebreaker

informed of any change in her ETA at the position where

escorting is to commence. Procedural information on how

to obtain icebreaker assistance through selected port or

harbour radios is given in Admiralty List of Radio Signals

Volume 6.

The channel

7.46

1 When an icebreaker is breaking a channel through large

heavy floes at slow speed, the channel will be about

30%–40% wider than the beam of the icebreaker. If,

however, the ice is of a type which can be broken by the

stern wave of the icebreaker proceeding at high speed, the

width of the channel may be as much as three times the

icebreaker’s beam.

2 In the channel there may be pieces of ice and small

floes which the icebreaker has broken off the floes at the

sides of the channel. These may greatly reduce the speed

of a ship following the icebreaker, or may even block the

channel.

3 Rams (Photograph 14, page 153) sometimes project into

the channel from old ice. A ship unable to keep off the ice

should request the icebreaker to widen the channel. But in

the narrow channel left by an icebreaker in heavy ice, rams

are less likely to be encountered.

Distance between ships

7.47

1 The Master of the icebreaker decides on the minimum

and maximum distances that a ship should keep from the

icebreaker.

The minimum distance is determined by the distance the

ship requires to come to a complete stop after reversing her

engines from full ahead to full astern. The maximum

distance depends on the ice conditions and the distance the

channel will remain open in the wake of the icebreaker.

If the escorted ship cannot maintain the distance ordered,

the icebreaker should be informed at once.

2 In ice concentrations of 7/10 and less, a ship can usually

keep station on the icebreaker with little difficulty. With an

ice concentration of 10/10, however, the track will tend to

close quickly behind the icebreaker necessitating a very

close escort distance. If such ice is under pressure, the

distance must be reduced to a few metres since the channel

will be quickly covered with ice, leaving only a small lead

astern of the icebreaker narrower than her beam. If there is

considerable pressure, progress may be impossible.

3 To force a passage through large floes and icefields, the

icebreaker may require to increase speed to strike the ice

and crush and break it ahead of her. A ship following her

must then watch the distance carefully and try to enter the

channel made by the icebreaker before it closes.

Courses

7.48

1 Before entering the ice the Master of the icebreaker will

decide on the route to be taken.

When course is altered, an escorted ship must follow

precisely in the wake of the icebreaker.

Alterations of course by the icebreaker are made as

gradually as practicable. When sharp turns are made, a ship

following the icebreaker is liable to swing into floes at the

side of the channel, or to get beset.

Speed

7.49

1 The speed of an escorted ship is ordered by the

icebreaker.

2 In open ice a speed of 6–7 kn can be expected to be

maintained, but only if it is certain that the ship will not

collide with the floes. A useful rule of thumb is that 8 kn

can be maintained in an ice concentration of 4/10 and that

the speed will be reduced by 1 kn for each additional 1/10

of concentration. However, thickness and hardness of the

ice, snow cover, puddling and ice under pressure may need

to be taken into consideration in addition to the ice

concentration.

3 In close ice, when the escorting distance is reduced, a

speed of no more than 5 kn should be attempted.

Stopping

7.50

1 When an icebreaker comes to a standstill and is unable

to make farther progress without coming astern, she shows

and sounds the appropriate signals. These signals should be

treated with extreme urgency. Engines should immediately

be put astern and the rudder used to reduce headway.

2 If a single-screw ship suddenly goes astern while

passing through a narrow channel through ice, she may

slew and damage her propeller and rudder on the ice. To

avoid collision with a ship ahead it is often preferable to

ram the ice on one side of the channel if it is sufficiently

thin to embed the bow without damage rather than risking

going astern.

3 Caution. Due to unexpected conditions or in emergency

an icebreaker may stop or manoeuvre ahead of an escorted

ship without any warning signal.

Towing

7.51

1 All icebreakers are fitted with towing winches with a

towing wire reeled on each winch drum. Each towing wire,

which has at it end an eye and a hauling-in pendant, is led

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over an indentation in the stern. The winches are sited as

far forward as possible to minimise the vertical angle of

tow, and to allow the stem of the ship being towed to be

hove close into the indentation in the icebreaker’s stern.

2 Icebreakers tow at either long or short stay. When

certain icebreakers tow at short stay, the towed vessel is

hauled close-up into an indentation or yoke at the

icebreakers stern, and for them, this is the most usual

method, particularly when the ice is uneven and the

icebreaker’s speed varies. Certain vessels, however, because

of their size or the construction of their stem, can only be

towed at long stay.

3 When an icebreaker decides to tow, the assisted ship

must immediately prepare to take on board and secure

quickly the towing wires, particularly if there is ice

screwing or ice pressure. Heaving lines passed to the after

deck of the icebreaker are used to bring inboard the

hauling-in pendants of the towing wires. These are brought

to the escorted ship’s capstan, so that the eyes of the

towing wires can be hauled aboard and secured. When the

towing wires are fast, the icebreaker is informed and the

forecastle cleared of all personnel.

4 When towing, the icebreaker decides at what speed the

towed ship’s engines should be run. The towed ship’s

rudder must be used to assist the icebreaker in holding her

course and in her other manoeuvres.

Casting off the tow must be done without delay,

particularly if towing from the ice into a heavy sea.

Breaking ships out

7.52

1 When an escorted ship becomes beset, she should

normally keep her engines moving slowly ahead to keep

ice away from the propellers.

In thin ice, the icebreaker usually comes astern along the

channel and cuts out ice on either bow of the ship. The

icebreaker then goes astern close along the whole length of

the lee side of the beset ship, and then goes ahead,

simultaneously ordering the ship to follow her.

2 In heavier ice, ships can usually be broken out by the

icebreaker turning through 180°, going back to the beset

ship and passing close aboard her leeward side. The

icebreaker then turns through 180° astern of her, and

returns along either, her leeward side to thin out the ice or

her windward side to relieve pressure on that side, at the

same time ordering the ship to follow her.

3 An alternative method, also used for a ship beset when

proceeding independently, is as follows. The icebreaker

approaches the beset ship on either quarter, passes along

her side, and crosses ahead of her at an angle of between

20° and 30° to the beset ship’s course. In moderate winds,

the manoeuvre may be made on either side: in strong

winds, the side will be determined by which vessel is most

influenced by the wind.

4 Having crossed ahead of the ship, the icebreaker goes

astern to crack any floe fragments left near the beset ship’s

stem, and then goes ahead ordering the beset ship to

follow, keeping in her propeller wash.

Convoys

7.53

1 If several vessels are to be assisted at the same time, a

convoy will be formed. The sequence of ships in the

convoy and their distance apart will be ordered before

entering the ice by the Master of the icebreaker.

Particular attention must be paid to maintaining the

distance ordered: it will vary with the ice conditions.

If a ship’s speed is reduced, the ship astern must be

informed immediately.

2 Ships ahead and astern, as well as the ice, must be

carefully watched.

Light and sound signals made by the icebreaker must be

promptly and correctly repeated by ships in the column in

succession.

EXPOSURE TO COLD

Effects on the body

General information

7.54

1 In severe low temperatures action must be taken to

protect the body and its extremities. It is most important

that minor injuries be treated immediately to avoid

complications. Minor cuts and skin abrasions provide a

ready entry for frostbite.

Skin contact with metal objects should be avoided.

Contact with steel at temperatures of –7°C and lower will

cause instant blistering.

2 Feet should be protected from blisters, frostbite and

“immersion foot” — a condition of painful swelling with

inflammation and open lesions caused by prolonged

exposure to low temperatures and moisture. Immersion foot

may be avoided by keeping the feet warm and dry, which

is also the only treatment possible should the complaint be

contracted. When treating the feet they should not be

rapidly rewarmed, and care should be taken to avoid

damaging the skin or breaking blisters; they should not be

massaged.

Frostbite

7.55

1 Low temperatures causing freezing of the fluid in the

tissues results in frostbite. Its initial stages are painless and

may only be detected by a companion noticing the typical

white patch on the skin or by the person affected feeling a

hard spot on his face; the usual parts of the face affected

are the nose, cheek bones, chin or ears. Such patches can

easily be cured by warming them with the hand until the

frozen fluid is melted, but it should be realised that it will

only be a matter of time before the trouble will recur

unless precautions such as using a hood or wind shield for

the face are taken. Care should be taken not to let the

hands get wet with petrol or oil.

2 The feet are also liable to frostbite and this is more

serious as they cannot be seen and the person affected will

only be warned after a while by the lack of feeling;

immediate action should be taken to restore the circulation.

A frostbitten part should never be massaged or rubbed with

snow.

Wind chill

7.56

1 The limitations imposed by winds at low temperatures

are shown in Diagram 7.56. They apply to those with

special clothing for use in low temperatures, which protects

all skin areas from direct wind with sufficient thickness to

prevent undue coldness; without proper clothing, the

limitations are of course greater.

2 The point of intersection of the appropriate wind speed

and temperature values gives the Wind Chill Factor, eg

Temperature –10°C and Wind Speed 20 mph give a Wind

Chill Factor of III.

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CHAPTER 7

177

Wind Chill

Factor

Indicates

I Comfortable with normal precautions.

II Work becomes uncomfortable on overcast

days unless properly clothed.

III Work becomes more hazardous even on

clear days unless properly clothed. Heavy

outer clothing is necessary.

IV Unprotected skin will freeze with direct,

exposure over a prolonged period,

depending on degree of activity, amount of

solar radiation and state of skin and

circulation. Heavy outer clothing becomes

mandatory.

V Unprotected skin can freeze in 1 minute

with direct exposure. Multiple layers of

clothing are mandatory. Adequate face

protection becomes important. Work alone

is not advisable.

VI Adequate face protection becomes

mandatory. Work alone must be prohibited

and supervisors must control exposure time

by careful scheduling.

VII Survival efforts are required. Personnel

become easily fatigued, and mutual

observations of companions is mandatory.

Clothing

7.57

1 If clothing gets wet in any way, or if hoar frost, which

is almost invisible, settles on it, it should be dried as soon

as possible.

Perspiration should be avoided since it soaks into the

clothing and ruins insulation qualities, as will any form of

moisture. Before starting arduous work, clothing should be

removed or opened up so that work is commenced “cold”.

As the work progresses, clothing should be replaced or

closed up until a comfortable body temperature is reached.

2 Panting, and the intake of large masses of cold air, can

lead to internal frostbite, and should therefore be avoided.

Frequent rest between spells of labour and breathing only

through the nose will help in this respect. A muffler or

scarf worn across the lower part of the face will also be of

value.

Gloves should be worn continually, even for delicate

jobs. They should always be worn on harness round the

neck with a cross-piece to prevent loss.

Snow-blindness

7.58

1 Ultra-violet light burning the cornea of the eye causes

snow-blindness. The ultra-violet reflected from snow and

ice must be excluded from the eyes whenever the sun is

above the horizon by wearing protective goggles or glasses.

In emergency, effective substitute goggles can be made

with cardboard or any other material cut into two ovals,

with narrow horizontal eye-slits and held in position with

string or cloth. Some protection may also be gained by

blackening the face about the eyes, nose and cheeks with

dirt, charcoal or soot.

2 One can become snow-blind in overcast or cloudy

conditions as easily as in direct sun since the ultra-violet

light is always present; one attack predisposes to another.

Symptoms appear some time after exposure when the eyes

smart and water, and soon feel as though they are full of

sand, and even blinking is painful. Severe pain will last at

least 24 hours, and during this time it is best to remain in

darkness, or keep the eyes bandaged.

Hypothermia

7.59

1 Under normal circumstances when wearing adequate

protective clothing hypothermia, which is the term for an

abnormally low body temperature, is unlikely to occur to a

healthy individual. But in extreme conditions when

exhaustion occurs, or when the insulative properties of

clothing are impaired through tearing or wetting from sweat

or water, or when the body is immobilised because of

injury, hypothermia is quite likely to occur. It may be

recognised by an intense feeling of cold, abnormal

29 25 21 17 13 9 5 1

-1 -5 -9 -13 -17 -21 -25 -29 -33 -37 -41

VII

III

TEMPERATURE °C

WIND

SPEED

m.p.h.

Wind Chill Diagram (7.56)

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CHAPTER 7

178

behaviour patterns, uncoordinated muscle movements which

may result in stumbling and the like, culminating in

unconsciousness and death.

2 Treatment consists of removing the victims from the

hypothermia environment, ie shelter, remove wet clothing

and replace with dry, wrap in blankets to insulate from the

cold, and provide some extra heat for the body. If

conscious, give plenty of hot sweet drinks and food if

possible. Victims are very likely to suffer relapses unless

special precautions are taken.

Immersion

General information

7.60

1 In polar waters the dangers of immersion experienced

elsewhere are accentuated by the colder water. Without

special clothing such as immersion suits, even short periods

of immersion in extremely cold water can be fatal.

Arrangements for abandoning ship should make provision

therefore for entry into life-boats or life-rafts by scrambling

nets or other means without entering the water.

2 The clothing worn, morale, physical fitness, injury or

loss of body heat at the time of immersion may cause wide

variations in the times of survival from unconsciousness or

from death.

For further details see, A Pocket Guide to Cold Water

Survival, published by IMO.

3 Approximate likely times of survival of those immersed

in light clothing are as follows:

Water Temp

(°C)

Survival Time

0°

20 minutes to 12 hours.

5°

30 minutes to 22 hours.

10° 1 hour to 4 hours.

15° Unconsciousness may occur about 2 hours

after immersion but death may not result

even after several hours.

20° Neither unconsciousness nor death may

result from cold exposure.

4 Rescuers of victims of drowning in cold water must

persist with resuscitation attempts for even longer than after

warm water drowning. One to two hours is recommended.

Signs of life are harder to detect because cold slows all the

body’s functions, and a cold victim has more chance of

surviving a long period before the heart is restarted.

It is not uncommon for survivors, apparently unharmed

when rescued from the sea at low or even moderate

temperatures, to die subsequently from heart failure

attributed to hypothermia.

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179

CHAPTER 8

OBSERVING AND REPORTING

HYDROGRAPHIC INFORMATION

General remarks

8.1

1 Ever since man ventured on the sea, mariners have

depended upon the experience and reports of those who

sailed before; in this way, through the years, an increasing

amount of information was accumulated from seafarers and

explorers until it became possible to set down the details in

convenient form, which was on the charts and in Sailing

Directions. It may be true to say that there are now no

undiscovered lands or seas and that most coasts have, to a

greater or lesser degree, been surveyed and mapped; yet it

is equally true that the accuracy of charts and their

associated publications depend just as much as ever on

reports from sea, and from others who are responsible for

inshore surveys, lights, and other aids to navigation.

Without a supply of information from these sources, it

would not be possible to keep the charts and publications

corrected for new and changed conditions.

2 Whenever a ship is making good a track over a portion

of the chart where no soundings are shown, or over an area

of suspected shoal depths, it is advisable to take soundings.

If the ship is fitted with a suitable echo sounder, such

soundings if properly recorded and reported, will be of

much value for improving the chart.

3 The planning of surveys can be considerably assisted by

reports from ships on the adequacy or otherwise of existing

charts, particularly in the light of new or intended

developments at a port. In this connection the views of

Harbour Authorities and pilots can be of value.

Sources of information

8.2

1 The world-wide series of charts and publications

maintained and sold by the United Kingdom Hydrographic

Office relies mainly on the following sources for compiling

and maintaining them.

The Royal Navy and other surveying organisations.

Foreign hydrographic offices and/or national charting

authorities.

2 Other functional authorities e.g. lighthouse and port

authorities.

Commercial organisations e.g. communications

companies, oil and gas operators.

Ships and shipping companies.

Private individuals e.g. leisure sailors.

3 Of these sources of information, the first four are to a

large extent automatic and provide the broad base of

necessary data, but the last two are no less important for

keeping the published information correct, since the

intervals between regular surveys may be very long.

Opportunities for reporting

8.3

1 Subject to complying with the provisions of international

law concerning innocent passage through the territorial sea,

or to national laws where appropriate, every mariner should

endeavour to note where charts and publications disagree

with fact and should report any differences to the United

Kingdom National Hydrographer. Statements confirming

charted and published information which may be old, but

nevertheless correct, are of considerable value and can be

used to reassure other mariners visiting the area.

2 It is hoped that the mariner, by following the points

mentioned below, will be able to make best use of the

opportunities with which he is often presented to report

information, though it is realised that all ships do not carry

the same facilities and equipment.

3 Reports which cannot be confirmed, or are lacking in

certain details, should not be withheld. Shortcomings

should be stressed, and any firm expectation of being able

to check the information on a succeeding voyage should be

mentioned.

RENDERING OF INFORMATION

Forms of reports

Hydrographic Note

8.4

1 Reports should be forwarded to the United Kingdom

Hydrographic Office, Admiralty Way, Taunton, Somerset,

TA1 2DN, United Kingdom. They can either be in

manuscript, e-mail or on Forms H.102 and H.102a (pages

180 and 185) which can be obtained gratis through any

Admiralty Chart Agent. Alternatively, copies included at the

end of every copy of Weekly Editions of Admiralty Notices

to Mariners, can be used. Admiralty List of Radio Signals

can be assisted in providing the latest details of maritime

radio services by new, additional or corroborative

information from users. Such information can be forwarded,

either in manuscript, e-mail or on the report form in the

front of each volume of Admiralty List of Radio Signals, or

on Form H.102.

Obligatory reports

8.5

1 Dangerous shoal soundings, uncharted dangers and

navigational aids out of order should be reported by the

Obligatory Report procedure (3.1), by radio or any other

available means to:

The nearest coast radio station;

2 United Kingdom Hydrographic Office, Radio

Navigational Warnings:

Phone: +44(0)1823 723315

Fax: +44(0)1823 322352

Telex: 46464 HYDRNW—G

e-mail: rnwuser@ukhornw.u-net.com

3 The draught of modern tankers is such that any

uncharted depth of less than 30 m may be of sufficient

importance to justify such action.

Some information, dependent on its source and

completeness, will require corroboration from an

authoritative source (e.g. primary charting authority, port

authority) before being acted upon. However, if

corroboration is being sought, but the nature of the

information is such that it needs to be promulgated

urgently, a Notice to Mariners (NM) may be issued.

4 Such reports should always be followed by a completed

Form H.102 giving all available information.

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